Electrical ignition and safety systems for burners



ELECTRICAL IGNITION AND SAFETY SYSTEMS FOR BURNERS Filed Oct. 10. 1955G. SCHWANK Sept. 13, 1960 4 Sheets-Sheet 1 A m m miknq v R w W M m WW 4QM a? k E all. mf .18.,

G. SCHWANK Sept. 13, 1960 ELECTRICAL IGNITION AND SAFETY SYSTEMS FORBURNERS Filed Oct. 10, 1955 4 Sheets-Sheet 2 ELECTRICAL IGNITION ANDSAFETY SYSTEMS FOR BURNERS Filed Oct. 10, 1955 G. SCHWANK Sept. 13, 19604 Sheets-Sheet 3 Sept. 13, 1960 G. SCHWANK 2,952,308

ELECTRICAL IGNITION AND SAFETY SYSTEMS FOR BURNERS Filed oct. 10, 1955 4Sheets-Sheet 4 assembly can assume;

U ted ews P fl i F ELECTRICAL IGNITION AND SAFETY SYSTEM FOR BURNERS 1Filed on. 10, 1955, Ser. No. 539,699

' '8 Claims. (Cl. 1 582 8)' This invention relates to electricalignition and safety systems for burners and particularly to electricalignition and safety systems for burners inwhich a thermostat actuated bythe heat within the burner controls the supply of fuel thereto. Y

One object of this invention is to provide an electrical ignition andsafety system which in theevent the heat of combustion actuating thethermostat therein should die out will almost immediately shut off thefuel supplyto the burner.

Another object of the present invention is to provide an electricalignition and safety system for burners which, in the event that theburner should cease operating, will almost immediately actuate theignition device in order to reignite the fuel being supplied to theburner.

Another object of the present invention is to provide a novel contactassembly for a thermostatically operated circuit controlling means inelectrical ignition and safety systems. V

A general object of this invention is to provide an electrical ignitionand safety system for fluid fuel burners which system is of novelconstruction and which is highly responsive to temperature conditionswithin the burner.

Other objects of this invention will become clear hereinafter as thecharacteristic features of construction and mode of operation of thisinvention are described i detail.

A In the drawings:

Fig. 1 is a diagrammatic view of an ignition safety system in whichthe'thermostat included therein controls both the supply of fuel to theburner and the ignition coil employed within the burner to ignite thefuel;

Fig. 2 shows diagrammatic views of the thermostatically controlledcontact assembly in a system of the type described illustrating threeconditions which said contact Fig. 3 is a longitudinal cross sectionalview of a com- I bined control switch and ignition carriage embodyingthe present invention;

Fig. 4 is a sectional view taken along the line 44 of Fig. 3; and H Fig.4a is a fragmentary sectional view similar to Fig. 4 illustratinganother form of the present invention.

The main parts of the system are the burner I typically located within aconventional combustion chamber, as schematically indicated by thebrokenline 0-0 in the drawing, the combined-igniter. and heat responsiveswitch 2' also typically located in .the combustion chamber, the controldevice 3' and the switch box 4'. Within the range of the fuel outlet ofburner 1 thereis-positioned the igniter or electrical ignition coil 5.ofthe assembly 2. As will later be seen from the description of Figs. 3and 4, the thermostat is exposed to the flame of burner 1 and, undercertain conditions, to ignition coil 5,. The thermostat itself is shownin Fig. 1; when heated, it will cause switch lever 6 with its contact 7tomove in .the ,direction of counter-contact 8. The remaining structural2,952,308 Patented Sept. 13, 1960 parts of the entire device aredescribed below in connection with their function.

. When the thermostat is cold, lever 6 and its contact 7', are in theposition shown in Fig. '20. When switch 13 is closed, current begins toflow from terminals 32 and 33 of'switch box 4' through the primarywinding 3.4 of the transformer 35 located in the control device 3. Topsecondary winding 36 draws current from the transformer 35 for theignition coil 5 which is fed to it by way of terminals 37a and 38a andthe respective terminals 37b and 38b and the two contacts 7 and 31.After a certain warm-up, contact 7' of lever 6 will, asshown in Fig. 2b,touch in addition contact 8 of the assembly 2', so that voltage isapplied also to the rectifier 27 and thereby to field winding 28 ofvalve 29 by way ofthe bottom secondary winding 39, and input terminals40a, "41a; 40b and 41b. The valve 29 will open, and the burner 1 will beignited by glowing ignition coil 5. 'When the thermostat is heatedfurther by the flame of the burner 1, contacts 7 and 31 are separated,as shown in Fig. 2c, and the current flow to ignition coil 5 isinterrupted.

When the burner 1 goes out, cont-act 7' will-after a slight cooling-offof the thermostat-move back into the position shown in Fig. 2a. Thevalve 29 will close, and the ignition coil 5 is made to glow. Thereupon,burner 1 may again be ignited by the ignition coil 5, provided that line30 receives fuel, and the process described is repeated.

In switch box 4', a resistance 42, is connected in parallel with signallight 16. With the heat responsive switch in the position shown in Fig.2a, the light will burn brightly, since the ignition current for theignition coil 5 flows through it and through resistance 42. When in theposition shown in Fig. 20, only the weak current for the field winding28 of valve 29 will flow through the switch box 4'; therefore, when theequipment is in continuous operation, bulb 16 will glow but dimly, thusindicating that valve 29 is open and ignition coil 5 is disconnected.

Figs. 3 and 4 show a constructional version of assembly 2'. The parts of.the assembly that are aifected by dust and corrosion are located in ahousing consisting of a cover 43 and the parts 44. and 45. To the cover43 there is attached, by means of screws 46, a. disk 47, made of aninsulating material. A metal sleeve 48 is soldered to cover 43. Aceramic, cylindrical rod 49 is movably mounted in this metal sleeve.This ceramicrod rests with its face 50 on a stop 51, of sleeve 48,consisting in the example shown of an indentation. A heater filament .52is wound around ceramic rod 49 and connected in series with the ignitioncoil 5. The ignition coil 5' is located in front of the face .50 of theceramiczrod 49. A metal plate 54 is fastened together with insulating-material disk 47 in the housing by means of screws 46, .in a slot 53of disk 47. [This plate carries two arms 55, whose outer edges arefitted with a knife-edge bearing 56 for a lever-like bracket 57. Thisbracket 57 is rotated by the ceramic rod 49 through the intermediary ofa metal pressure, plate 58, and a ball 60, whose position may beadjusted by a set screw 59. It is further subject to the action of areturn spring 61. The arm 62 from which it is suspended is also fittedto the metal plate'54. The other free end of bracket 57 has an eye inwhich a contact pin 7 is movably mounted. The con-, tactpin has anenlarged head 65 for an end stop .By means .of a spring wire 66, that isattached to bracket 57 and leads around the eye 63, and which in notch67 exerts a pressure upon pin 7', a certain friction is exerted upon pin7. Contact pin 7 works with two counter-contacts 31 and 8, each. ofwhich is fastened to a. spring strip 70 or 71,respective1y. Strip 70,together with two angle brackets 72 and 73, strip 71 together with asingle angle bracket 74, are attached by means of a screw 75 each to adisk 76, made of an insulating material. To accommodate the end of screw77, which connects-housing parts 44 and 45, a longitudinal groove 78 isprovided in disk 76. Disk '76 is connected with disk 47 by means of'twospacer bolts, 79 and 80. Only spacer bolt 79 is visible in Fig. 3, whileFig. 4 shows both spacer bolts. Four threaded metal'pieces, 81, 82, 83and 84, are set into disk 76. The two mounting screws 75 are screwedinto threaded pieces 81 and 82, while the spacer bolts 79 and 80 arescrewed into threaded pieces 83 and 84. At the opposite end of eachthreaded insert, there is a terminal screw 85, for the four currentsupply leads (terminals 37b, 38b, 40b and 41b of Fig. l) which arebrought into the ignition-cartridge housing through throat 86. The twocurrent-supply lines of heating filament 52 and ignition coil 5 areconductively connected with the two spacer bolts 79 and 80. Conductivelyconnected to spacer bolt 79, byway of suspension arms 62 and returnspring 61, is also bracket 57.

The two spring strips 76 and 71, to which countercontacts 31 and 8 areattached, are bent to a right angle at their free ends and fitted withslots 87 and 88, respectively, to accommodate the free ends of anglebrackets 72 .and 74. Thus, spring strips 70 and 71 are only able to moveover a range determined by the height of slots 87 and 88 and thethickness of angle brackets 72 and 74. The top counter-contact 31 may beadjusted by means of a setscrew 89, which is threaded into angle bracket73 and will deviate angle bracket 72, elastically deforming it whatdifierent construction of the end of the device facing the burner. Forin this version, the heating filament 90 is wound around the metalsleeve 48' that houses the ceramic rod 49' and a stop 51' therefor.Thus, the heating filament 90 serves at the same time as an ignitioncoil. The head of the device is contained within an additionalsheet-metal housing part 91. The heating filament 90 is held by screws92 in the threaded metal pieces 93 and 94. These threaded metal piecesin turn are screwed onto spacer bolts 79 and 80. Thus, spacer bolts 79and 80 serve in both cases, that is, regardless of whether the heatingfilament is located inside metal sleeve 48 or outside of it, as acurrent-supply line for heatnig filament and ignition coil. This versionoffers the advantage that the ignition coil used for the heating may bereadily replaced.

The device operates as follows:

Counter-contact 31 is connected with the terminal marked 37b in Fig. 1.Counter-contact 8 is connected to terminal 40b. The two spacer bolts 79and 80 are connected to input terminals 38b and 41b, respectively. Solong as metal sleeve 48 is not heated up, the parts of the device are inthe position shown in Fig. 3. Now when circuit breaker 13 (Fig. 1) isclosed, current is supplied to heating filament 52 and to ignition coil5 or to heating filament 90, respectively, which is made to glow. Thiscauses metal sleeve 48 to heat up and to expand. Ceramic rod 49,supported by stop 51 of metal sleeve 48, follows this movement, asreturn spring 61, by way of bracket 57, forces it towards the left. Theright-hand, free end of bracket 57 is thereby moved downward, and withit contact pin 7. Spring strip 70 and countercontact 31 first followthis movement, so that voltage continues to be applied to the heatingfilament and the ignition coil. After a certain shifting, contact pin 7will strike also counter-contact 8. Valve 29' of fuelsupply line 30 isthereby opened and burner 1 is ignited. The flame of the burner willheat up metal sleeve 48 further, and bracket 57 is further swungdownward with its free end. The upper edge of slot 87 then comes to reston angle bracket 72, and contact pin 7' is removed from counter-contact31. Heating filament 52 and ignition The cross-section shown in Fig. 4aillustrates a somecoil 5 or heating filament 90, respectively, aredisconnected. As metal sleeve 48 is heated further, spring strip 71 ispressed downward, since its spring action is less than the friction bywhich contact pin 7' is kept in eye 63. However, as soon as the upperedge of slot 88 reaches angle bracket 74, pin 7upon a further swingingof bracket 57;is pushed into eye'63. Thus, there will be no furtherchange in the distance between head 65 of contact pin 7' and topcounter-contact 31. When the flame to which metal sleeve 48 is exposedgoes out, the free end of bracket 57 will move upward. After a slightswinging movement determined by the height of slot 88 in spring strip71, the contact between contact pin 7 and counter-contact 8 is broken,and valve 29 in fuel-supply line 30 is closed. Contact pin 7' thenstrikes top counter-contact 31, and current is supplied to the ignitioncoil. Voltage will be applied to the ignition coil until burner 1 isagain ignited.

The temperature at which valve 29 is to op en may be set at screw 59 ofbracket 57. Insertion to ball'60 and knife-edge 56 suspension of bracket57 render the movement of bracket 57 nearly frictionless. Because of thefact that knife-edge bearing 56 is located in close proximity to thepoint of contact between bracket 57 and the thermostat, the expansion ofmetal sleeve 48 is transmitted to contact pin 64 considerably magnified.The ditference between the temperature at which valve 29 is to open andthe temperature at which the ignition current is to be shut off may beset at screw 89.

In place of the frictional force applied in the constructional exampleshown in the drawing and counter to which the contact holder is slidablymounted between the counter-contacts, a magnetic field, or friction anda magnet, may be employed without deviating from the principle of theinvention. 7 v

It is believed clear from the foregoing description that an electricalignition and safety system has been provided herein in which in theevent that the flame in the burner should die out, when there has been a'very slight cooling of the thermostat the fuel supply line is shut off,and under certain conditions the ignition device is put into immediateoperation in order to reignite the burner upon resumption of the fuelsupply.

Although I have herein shown and described several forms of the presentinvention, it will be understood that various changes and modificationsmay be made therein within the scope of the appended claims withoutdeparting from the spirit and scope of this invention.

What is claimed is:

1. In a control system for a fluid fuel burner having a combustionchamber, an electrical ignition and safety device comprising athermostat adapted to be responsive to combustion chamber temperature ofthe burner, circuit controlling means for controlling a fuel supply tothe burner, said circuit controlling means including a movable contactassembly, and first and second companion contacts, said movable contactassembly comprising a movable member actuated by said thermostat, saidmovable member having an aperture therein, a pin disposed in saidaperture for longitudinal slidable movement relative to said movable.member, and a spring secured to said movable member and frictionallyengaging said pin for yieldably holding said pin in fixed relation tosaid movable member, said companion contacts being arranged in spacedconfronting relation and being adapted to be engaged by opposite ends ofsaid pin to selectively close contact therewith in response to movementof said movable member, said movable member being movable relative tosaid pin against the force of said spring. when said 'pin is inengagement with said second companion contact whereby to preventexcessive movement of said pin away fromsaid first counter-contact andmeans .biasing'said first contact against the end of said pin adjacentthereto for maintaining said first contact in engagement with saidadjacent pin end for a predetermined movement of said movable memberaway from said first contact duringfpart of which predetermined movementthe end of said pin adjacent said second contact is in engagement withthe latter. I

2. In a control system for a fluid fuel burner having a combustionchamber, an electrical ignition and safety device comprising athermostat having an element adapted to be movable in response tocombustion chamber temperature changes of said burner, a pivotallymounted bracket operatively engaging said movable thermostat element atone end and movable thereby and, having an aperture at its opposite end,a pin disposed in said aperture for longitudinal slidable movementrelative to said movable member, and means for yieldably holding saidpin in fixed relation to said movable member, said companion contactsbeing arranged in spaced confronting relation and being adapted to beengaged by opposite ends of said pin to selectively close I contactstherewith in response to movement of said movable-member, said movablemember being movable relative to said pin against the force of saidyieldable holding means when said pin is in engagement with said secondcompanion contact whereby to prevent excessive movement 'of said pinaway from said first counter-contact and means biasing said firstcontact against the end of said pin adjacent thereto for maintainingsaid first contact in engagement with said adjacent pin end for apredetermined movement of said movable member away from said firstcontact during part of which predetermined movement the end of said pinadjacent said second contact is in engagement with the latter. I

3. In a control system for a fluid fuel burner having a combustionchamber, an electrical ignition'and safety device comprising athermostat having an element adapted to be movable in response tocombustion chamber temperature changes of said burner, a bracketpivotally mounted on knife edges adjacent one end thereof andoperativelyengaging said movable thermostat at said one end, saidbracket having an aperture therein adjacent its other end, said otherend of said bracket being relatively remote from said knife edgemounting whereby a small movement of said thermostatelement induces. arelatively large movement of said other end of said bracket, a pindisposed in said aperture for longitudinal slidable movement relative tosaid movable member, and means to yieldably holding said pin infixed-relation to said movable member, said companion contacts beingarranged in spaced confronting relation and being adapted to beengagedby opposite ends of said pin to selectively close contact therewith inresponse to movement of said movablemember, said movable member beingmovable relative to said pin against the force of said yieldableholdingmeans when said pin'is in engagement with said second companion contactwhereby to prevent excessive move- ,55

ment of said pin avvayfrom said first counter-contact and means biasingsaid first contact against the end of said pin adjacentthereto formaintaining said first contact in engagement with said adjacent pin endfor a predetermined movement of said movable member away from said:first contact during part of which predetermined movement the end ofsaid pin adjacent said second contact is in engagement with the latter.v Y

4. In a control system for a burner using fluid fuel and having a fuelsupply line extending into said burner, an electrical'ignition andsafety device comprising a thermostat including a metallic tube having ashoulder at one end and a ceramic core slidably mounted in said tube andengaging said shoulder at one end and extending out of said tube attheother end wher eby saidother en d of said core moves relativet'o thecorrespondingen'd of said tube when the thermostat is subjected .totemperaturechange; and circuit controlling means comprising -a brackethaving the form of a two armed lever, said bracket being pivotallymounted adjacent one end thereof and said one 1 "'6 .e'nd operativelyengaging said other end of said ceramic rod whereby a'relativelysmallmovement of said ceramic rod induces a relatively large movement ofthe, other end oftsaidbracket, said other end of said bracket having anaperture therein, a'contact pin slidably mounted in said aperture, aspring secured to said bracket and frictionally engaging said cont-actpin foryieldably holding said conitactpin in fixed relation to saidbracket, first and second icounter contacts, arranged in spacedconfronting relation and being adapted to be selectively engaged byopposite ends o'f'said pin in response to movement of said movable:member, said movable member. being movable relative to said pin againstthe force of said yieldable holding means when said pin is in engagementwith said s'econd'companion contact whereby to'prevent excessivemovement of. said pin away from said first'countencontact,an'ignitionfcoil for igniting fuel in'the'burner combustion chamber anddisposed in front of said first end of said metal tube, said ignitionco'il being constituted'by a heating coil wound on said metal tube forheating said thermostat, circuit means for simultaneously energizingsaid heating and ignition coils, said thermostat and said circuitcontrolling means being so arranged that when the temperature of saidthermostat'is; above apredetermined value said second-contact isengaged, said heating -coil when energizedand said fuel whenignited'being effective to heatsa'id thermostat above saidgiventemperature, engagement of said pin with saidsecond contact beingoperative to energize valve circuit means which include said secondcontact for opening an electrically operated valve in said valvecircuitmeans to permit the fuel to flow into'therburn'er, said pin andsaid first contact being parts iofsaidfheating andignition coil circuitmeans whereby iinterengagenientthereof energizes the latter.

5. InaFcon'trol s'ystemfor'a'burn'er using fluid .fuel and hatvingia"fuel supply line. extending into'said'burner, an electrical ignitionandsafetydevice comprising a thermostat .-'including a metallictubehaving a shoulder at one end and 'a-ceramic core slidably mounted insaid tube and engaging'said'shoulder at one end and extending outofsaidjtube at the other en'dwhe'reby said other end of said core. movesrelativetoithecorresponding end of said tube when the thermostat issubjected to temperature change; and circuit controllingmeans'co'mprisinga bracket having-the-form 'of a two.armed lever, saidbracket bein'g pivotally mounted. adjacent one end thereof and said oneend operatively engaging saidlother end of said ceramic rod whereby arelativelysmall movement of said ceramic rodinducesarelativelylargemovement of the other end of said bracket, said other endof said bracket having an aperture therein; a contact pin slidablymounted in said aperture, 'aspring secured to said:bracket andfrictionally engaging said contact pin for yieldably holding saidcontact pin in fixed relation to said bracket, first and second countercontacts arranged in spaced confronting relation and being adapted to beselectively engaged by opposite ends of said pin in response to movementof said movable member, said movable member 'being movable relative tosaid pin against the force of said yieldable holding means when said pinis in engagement with said second conipanioncontact whereby to preventexcessive movement of said pin away from said first counter-contact, aheating andignition coil wound on said thermostat tubeadjacent said'oneend thereoficircuit means for energizing said heating and ignition coil,said pin and said first contact being parts of said last mentionedcircuit means whereby interengagement thereof energize's'said heatingand ign'i- 11011 coil, said thermostat and said circuit controllingmeans being so arranged'that when the temperature of said thermostat isabove a predetermined value said second contact is engaged, said heatingcoil when energized and said fuel when ignited being effective to heatsaid thermostat above said given temperaturerengagement of --sa1d "pmsaid second contact being operative to energize valve circuit meanswhich include said second contact for opening an electrically operatedvalve in said valve circuit means to permit the fuel to flow into havinga fuel supply line extending into said burner, an

electrical ignition and safety device comprising a thermostat includinga metallic tube having a shoulder at one end and a ceramic core slidablymounted in said tube and engaging said shoulder at one end and extendingout of said tube at the other end whereby said other end of said coremoves relative to the corresponding end of said tube when the thermostatis subjected to temperature change; and circuit controlling meanscomprising a bracket having the form of a two armed lever, said bracketbeing pivotally mounted adjacent one end thereof and said one endoperatively engaging said other end of said ceramic rod whereby arelatively small movement of said ceramic rod induces a relatively largemovement of the other end of said bracket, said other end of saidbracket having an aperture therein, a contact pin slidably mounted insaid aperture, a spring secured to said bracket and frictionallyengaging said contact pin for yieldably holding said contact pin infixed relation to said bracket, first and second counter-contactsarranged in spaced confronting relation and being adapted to beselectively engaged by opposite ends of said pin in response to movementof said movable member, said movable member being movable relative tosaid pin against the force of said yieldable holding means when said pinis in engagement with said second companion contact whereby to preventexcessive movement of said pin away from said first counter-contact, anignition coil for igniting fuel in the burner combustion chamher anddisposed in front of said first end of said metal tube, a heating coilwound on said metal tube for heating said thermostat, said thermostatand said circuit controlling means being so arranged that when thetemperature of said thermostat is above a predetermined value saidsecond contact is engaged, said heating coil when energized and saidfuel when ignited being effective to heat said thermostat above saidgiven temperature, engagement of said pin with said second contact beingoperative to energize valve circuit means which include said secondcontact for opening an electrically operated valve in said valve circuitmeans to permit the fuel to flow into the burner, said thermostat andsaid circuit controlling means being further arranged so that said firstcontact is engaged when the temperature of said thermostat is belowanother given temperature, and circuit means closed only when said firstcontact is engaged for energizing said heating coil and said ignitioncoil, said other given temperature being greater than said giventemperature, whereby said first and second contacts are at times bothengaged.

ing out of said tube at the other end whereby said other end of saidcore moves relative to the corresponding end of said tube when thethermostat is subjected to temperature change; and circuit controllingmeans comprising a bracket having the formof a two armed lever, saidbracket being pivotally mounted adjacent one end thereof and said oneend operatively engaging said other end of said ceramic rod whereby arelatively small movement of said ceramic rod induces a relatively largemovement of the other end of said bracket, said other end of saidbracket having an aperture therein, a contact pin slidably mounted insaid aperture, a spring secured 'to said bracket and frictionallyengaging saidcontact pin for yieldably holding said contact pin in fixedrelation to said bracket, first and second counter-contacts arranged inspaced confronting relation and being adapted to be selectively engagedby opposite ends of said pin in response to movement of said movablemember, said movable member being movable relative to said pin againstthe force of said yieldable holding means when said pin is in engagementwith said second companion contact whereby to prevent excessive movementof said pin away from said first counter-contact, a heating and ignitioncoil wound on said thermostat tube adjacent said one end thereof, saidthermostat and said circuit controlling rneans being so arranged thatwhen the temperature of said thermostat is above a predetermined valuesaid second contact is engaged, said heating coil when energized and thefuel when ignited being effective to heat said thermostat above saidgiven temperature, and circuit means including said second contactclosed when said second contact is engaged for opening an' electricallyoperated valve in said last mentioned circuit means to permit fuel toflow into the burner, said thermostat and said circuit controlling meansbeing further arranged so that said first contact is engaged when thetemperature of said thermostat is below another given temperature, andcircuit means closed only when said first contact is engaged forenergizing said heating coil and said ignition coil, said other giventemperature being greater than said given temperature, whereby saidfirst and second contacts are at times both engaged.

8. In a control system for a burner using fluid fuel and having a fuelsupply line, a thermal responsive means for said burner, first andsecond contacts controlled by said thermal responsive means and eachhaving first and second conditions thereof, respectively, said firstcontact assuming said first condition thereof unless the temperature ofsaid thermal responsive means is above a first given value, said secondcontact assuming said first condition thereof unless the temperature ofsaid thermal responsive means is above a second given value which isless than said first given value, whereby when heating said thermalresponsive means said second contact assumes said second conditionthereof while said first contact is still in said first conditionthereof and upon cooling said thermal responsive means said firstcontact assumes said first condition while said second contact is stillin said second condition thereof, a heating coil for said thermalresponsive means and an ignition coil for igniting fuel in the burner,the heat from said heat ing coil and from ignited fuel being suflic-ientto heat said thermal responsive means to above said given temperaturewhereby to operate said contacts to said second conditions thereof,respectively, a solenoid operated valve which is open when said solenoidis energized, said valve being adapted to be disposed in the fuel supplyline for controlling the supply of fuel to the burner, first circuitmeans for energizing said heating and ignition coils closed only whensaid first contact is in its first condition, second circuit means forenergizing said solenoid closed only when said second contact is in itssecond condition, said heating and ignition coils being a relativelyheavy load as compared to said solenoid, whereby a relatively largecurrent flows through said first circuit means when said heating andignition coils are energized and a relatively small current flowsthrough said second circuit means when said solenoid is energized, asupply line for said circuit means in which the current flowing isrelatively large when said first circuit means is closed and relativelysmall when said first circuit means is open and said second circuitmeans is closed, and indicating means responsive to the supply linecurrent for indicating the condition of said first and second circuits,respectively.

References Cited in the file of this patent UNITED STATES PATENTS (Otherreferences on following page) 9 UNITED STATES PATENTS Harrington Jan. 1,1935 Maynard Apr. 9, 1940 Taylor Sept. 15, 1942 Hall May 7, 1946 ArantMar. 11, 1947 10 Korsgren Sept. 20, 1949 Eaton Feb. 14, 1950 Cerny eta1. July 25, 1950 Bongiorno Nov. 1, 1955 FOREIGN PATENTS Germany Nov. 5,1930

